A new version of Avast Business Managed Antivirus is scheduled for release on September 17th, 12:00 UTC.
Since September 10th the version 18.6 has been available for new installations only. Starting this rollout your AV will be updated automatically in following few days (according to your settings).
*Note: a restart of the workstation may be required.
Release notes - http://bit.ly/2CFRH9g